For example, Japanese Patent Laying-Open No. 2010-124557 (PTD 1) discloses an uninterruptible power supply apparatus including a converter, an inverter, and a DC step-up/step-down device. The converter converts AC power supplied from a commercial AC power source into DC power. The inverter converts DC power into AC power and supplies the converted AC power to a load. During a normal time when AC power is supplied from the commercial AC power source, the DC step-up/step-down device supplies DC power produced in the converter to a storage battery, and during a power failure time when supply of AC power from the commercial AC power source is stopped, the DC step-up/step-down device supplies DC power from the storage battery to the inverter. Thus, in the case of a power failure, the operation of the load can be continued as long as DC power is stored in the storage battery.